1. Field of the Invention
The present invention relates to an expansion valve equipped for example to an air conditioner of a vehicle, for controlling the flow rate of a refrigerant sent toward an evaporator, the expansion valve having a mechanism for discharging the refrigerant to the atmosphere in case of an emergency.
2. Description of the Related Art
Recently, a refrigerant used in a refrigeration cycle is required to have a property applying small load on the environment. However, some types of refrigerants are harmful to the human body or are inflammable.
In a refrigeration cycle using such types of refrigerant, in case of an emergency such as when the refrigerant is filled in a chamber due to gas leak or when gas leak occurs by collision of the vehicle, it becomes necessary to discharge the refrigerant rapidly into the atmosphere.
Non-patent document 1; Jul. 15-17, 2003 SAE Automotive Alternate Refrigeration Systems, “R-152a Mobile A/C with Directed Relief Safety System”, Mahmoud Ghodbane, Ph. D., James A. Baker, William R. Hill and Stephen O. Andersen, Ph. D.; discloses a refrigeration cycle for discharging the refrigerant to the atmosphere at times of emergency.
FIG. 2 shows an example of a refrigeration cycle circuit according to the above-mentioned prior art.
The prior art refrigeration cycle illustrated in FIG. 2 is formed of a compressor 1, a condenser 2, an expansion valve 3 and an evaporator 4 which are connected in the named order via a piping 7, wherein a first relief valve 5 is connected to a pipe branched out from the piping between the compressor 1 and the condenser 2, and a second relief valve 6 is connected to a pipe branched out from the piping between the expansion valve 3 and the evaporator 4.
As shown in FIG. 2, relief valves are disposed at two locations in the circuit, one in a high-pressure circuit connecting the compressor and the expansion valve, and one in a low-pressure circuit connecting the expansion valve, the evaporator and the compressor. In case of an emergency, signals are received from a refrigerant detection sensor for detecting refrigerant leak or from an acceleration sensor that operates during collision, based on which the relief valves are opened and refrigerant is discharged.
The reason why two relief valves are equipped in the prior art refrigeration cycle is because the high-pressure circuit and the low-pressure circuit are cut off when the air conditioner is stopped, since the valve of the expansion valve is closed. Therefore, if only one relief valve is disposed in the high-pressure refrigerant circuit, only the refrigerant in the high-pressure circuit can be discharged but the refrigerant in the low-pressure circuit cannot be discharged.
If one relief valve is disposed in the low-pressure circuit, the refrigerant in the low-pressure circuit can be discharged, and at that time, the discharge of the low-pressure refrigerant causes the pressure in the low-pressure circuit to drop, causing the valve of the expansion valve to open and the high-pressure refrigerant to flow into the low-pressure circuit. This causes the pressure in the low-pressure circuit to rise and the valve of the expansion valve to close, then the refrigerant in the low-pressure circuit is discharged through the relief valve, and when the pressure in the low-pressure circuit drops, the valve of the expansion valve opens again. This repeated phenomenon causes the refrigerant to be discharged gradually, or in other words, slowly, taking a long time to discharge the refrigerant.
Therefore, the refrigerant is discharged from both the high-pressure circuit and the low-pressure circuit, as illustrated in the refrigeration cycle of FIG. 2.